public interface IOperation
{
    public int Calculate(int a, int b);
}

public class AddOperation : IOperation
{
    public int Calculate(int a, int b)
    {
        return a + b;
    }
}

public class SubOperation : IOperation
{
    public int Calculate(int a, int b)
    {
        return a - b;
    }
}

public class MultiplicationOperation : IOperation
{
    public int Calculate(int a, int b)
    {
        return a * b;
    }
}

public class DivisionOperation : IOperation
{
    public int Calculate(int a, int b)
    {
        return a / b;
    }
}